1. Field of the Invention
The invention is directed to a system for controlling crowd when loading a hydrostatic loader. More specifically, an electronic controller and three pressure sensing switches are used to modify hydrostatic transmission output to reduce crowd when the loader approaches a stall condition.
2. Description of the Prior Art
Loaders are used to lift and move bulk materials. The loader comprises a self-propelled vehicle having a front mounted bucket and associated hydraulic lifting means for lifting the bulk material holding bucket. Such loaders may be provided with endless tracks of wheels to provide tractive force. Typically, the operator will drive the bucket into the bulk material and tilt and lift the bucket to shear the material away from the pile. The operator will then dump his load where desired and repeat the process as necessary.
During the loading operation, the loader develops two basic forces, a horizontal crowd force and a vertical lifting force. The crowd force is the reaction which results from the vehicle driving the bucket horizontally into the pile of material, whereas the lifting force is the reaction to the force required to lift the material from the pile. It is desirable to limit crowd reaction force such that significant lifting force remains.
Typically, loaders have been equipped with open center hydraulic systems. Such loaders have been designed to give priority for power to the hydraulic lifting means at the expense of the drive assembly. Since the bucket is close to a stall condition when digging, the power going to the hydraulic lifting means is absorbed as heat in the hydraulic system.
With energy efficient hydraulic systems, that is, power on demand hydraulic systems, the ability of loaders to relax crowd by consuming power thermally, is lost. Therefore, power not being consumed hydraulically would go the drive assembly resulting in increased crowd or excessive track spin if traction with the ground has been broken.
The object of the present invention is to provide a crowd control system for a loader using a hydrostatic transmission and a power on demand hydraulic system.